Production of hydroxy compounds by hydrogenolysis of buffered carboxylate salts

ABSTRACT

Carboxylic acids are converted to the corresponding hydroxymethylsubstituted compounds by preparing an aqueous solution of their alkali metal salts buffered to a pH between about 6.0 and 7.0 and then reacting the buffered salt solution with hydrogen in the presence of a hydrogenolysis catalyst such as active metallic cobalt. In a particularly useful embodiment the potassium salts of carboxylic acids, dicarboxylic acids, and hydroxycarboxylic acids having at least about four carbon atoms are hydrogenolyzed in a reactor within which the desired buffering is accomplished with potassium bicarbonate in the presence of a finite concentration of free carbon dioxide. After the reaction step the liquid product is degassed at a temperature high enough to decompose potassium bicarbonate to potassium carbonate; the reaction product separates into two phases because of the salting-out action of the resulting potassium carbonate, and the organic products can be recovered by decantation while the aqueous phase, containing reuseable potassium carbonate, is recycled to the acid-neutralization step which precedes the hydrogenolysis.

nited States Patent Hobbs et al.

[ 1 Dec. 17, 1974 1 PRODUCTION OF HYDROXY COMPOUNDS BY HYDROGENOLYSIS OFBUFFERED CARBOXYLATE SALTS [75] Inventors: Charles C. Hobbs; John A.Bedford,

both of Corpus Christi, Tex.

[73] Assignee: Celanese Corporation, New York,

[22] Filed: Dec. 15, 1972 [21] Appl. No.: 315,385

Related US. Application Data [62] Division of Ser. No. 64,665, Aug. 17,1970, Pat, No.

[52] US. Cl.... 260/635 D, 260/638 A [51} Int. Cl. C070 29/00 [58] Fieldof Search 260/635 D, 638 A [56] References Cited UNITED STATES PATENTS2,043,708 6/1936 Pruckner 260/638 A 2,121,367 6/1938 Schiller 260/638 A2,121,368 6/1938 Shiller 260/638 A 2,607,807 8/1952 Ford 260/635 D3,280,199 10/1966 Schmerling 260/638 A 3,344,196 9/1967 Corr et a1.260/635 D 3,478,112 11/1969 Adam et a1. r 260/635 D 3,524,892 8/1970Horlenko et a1... 260/637 R 3,752,861 8/1973 Hobbs et a1 260/635 DPrimary Examiner-Joseph E. Evans Attorney, Agent, or Firm-Ralph M.Pritchett [57] ABSTRACT Carboxylic acids are converted to thecorresponding hydroxymethylsubstituted compounds by preparing an aqueoussolution of their alkali metal salts buffered to a pH between about 6.0and 7.0 and then reacting the buffered salt solution with hydrogen inthe presence of a hydrogenolysis catalyst such as active metalliccobalt. In a particularly useful embodiment the potassium salts ofcarboxylic acids, dicarboxylic acids, and hydroxycarboxylic acids havingat least about four carbon atoms are hydrogenolyzed in a reactor withinwhich the desired buffering is accomplished with potassium bicarbonatein the presence of a finite concentration of free carbon dioxide. Afterthe reaction step the liquid product is degassed at a temperature highenough to decompose potassium bicarbonate to potassium carbonate; thereaction product separates into two phases because of the salting-outaction of the resulting potassium carbonate, and the organic productscan be recovered by decantation while the aqueous phase, containingreuseable potassium carbonate, is recycled to the acid-neutralizationstep which precedes the hydrogenolysis.

5 Claims, N0 Drawings PRODUCTION OF HYDROXY COMPOUNDS BY HYDROGENOLYSISOF BUFFERED CARBOXYLATE SALTS This is a division of application Ser. No.64,665, filed Aug. 17, 1970 now US. Pat. No. 3,752,861.

BACKGROUND OF THE INVENTION This invention relates to the conversion ofcarboxylic acids to the corresponding hydroxymethyl-substitutedderivatives by hydrogenolysis of the carboxyl group to the hydroxymethylgroup. More particularly it relates to a method for effecting suchhydrogenolyses which does not require either the esterification of thecarboxyl group as an initial process step nor the hydrogenolysis of thefree carboxylic acid with the attendant drawbacks of process apparatuscorrosion and resulting catalyst deactivation by corrosion products.

In a particularly useful embodiment this invention relates to a methodfor hydrogenolyzing unesterified carboxylic acids which, as comparedwith the prior art, is characterized by reduced energy requirements anda simplified process flow scheme in the product-recovery operationsfollowing the hydrogenolysis step.

It is known in the art to convert carboxylic acids to the correspondinghydroxymethyl-substituted compound by hydrogenolysis. Such processes areemployed, for example, for the conversion of adipic acid,o-hydroxycaproic acid, and their homologs to the corresponding diods,l,6-hexa nediol produced by such a method being a useful intermediatefor the production (by reductive amination) of hexamethylenediamine,which is used in the manufacture of nylon salt. Simply monocarboxylicacids can also be converted to monohydric alcohols by the same method.Processes of this nature as heretofore carried out, however, have haddrawbacks which are due to the acidity of the carboxylic acidfeedstocks. Specifically, with many hydrogenolysis catalysts, such ascopper chromite, catalyst deactivation by the free carboxylic acidnecessitates esterification of the acid as a preliminary step beforehydrogenolysis. Accomplishing the requisite substantially completeesterification necessitates the use of comparatively complicated andexpensive process apparatus and also requires the use of substantialquantities of energ). e.g., steam. Alternatively, methods are known forhydrogenolyzing the unesterified acids by employing as hydrogenolysiscatalyst rhenium black or pellets of sintered cobalt oxide which arereduced to metallic cobalt prior to the hydrogenolysis. Such catalystscan be employed for extended periods of time but have drawbacks in thatthey are comparatively expensive. Also they tend to become deactivatedultimately, either by the free carboxylic acid itself or by corrosionproducts resulting from interaction between the free carboxylic acid andthe metals of which the process apparatus is fabricated and strongsolutions of free carboxylic acid feedstocks aso cause the catalystpellets to disintegrate. Thus the process of the prior art have beencharacterized by either the expense of preparing ester intermediates or,alternatively, the corrosion-relation difficulties of handling freecarboxylic acids at the elevated temperatures characteristic ofhydrogenolysis processes.

It is an object of the present invention to provide a method foreffecting the hydrogenolysis of a carboxysubstituted compound to acorresponding hydroxymethyl-substituted derivative without the necessityof first converting the carboxylic feedstock to an ester. Likewise it isan object to provide a method for effecting such hydrogenolysis underconditions such that the contents of the hydrogenolysis reactor are ofdiminished acidity as compared with the conditions obtaining when suchdirect hydrogenolysis is carried out under the conditions characteristicof the prior art with resulting increase of catalyst life. It is anotherobject to provide a method for hydrogenolyzing an aqueous solutioncomprising a carboxylic acid having at least about 4 carbon atoms in themolecule whereby, at the conclusion of the hydrogenolysis step, theproducts can be separated from the aqueous component of the reactionmixture by a simple decantation method not requiring distillation orevaporation. It is a particular object to provide an improved method forproducing 1,6-hexanediol from adipic acid, o-hydroxycaproic acid,epsilon-caprolactone, or a mixture of these as formed in theliquid-phase oxidation of eyclohexane.

Other objects of the invention will be apparent from the followingdetailed description, examples, and claims.

SUMMARY OF THE lNVENTlON In accordance with the present invention acarboxysubstituted feed-stock, which may be a monocarboxylic acid, adicarboxylic acid, a hydroxycarboxylic acid, or a lactone (which is theequivalent of a hydroxycarboxylic acid in the present context), isneutralized in aqueous solution with a basic alkali metal compound,especially with potassium; the resulting solution of the metal salt ofthe carboxylic acid feedstock is then buffered to a pH between about 6.0and about 7.0, and the resulting buffered solution is then subjected tocatalytic hydrogenolysis to form the hydroxymethyl-substitutedderivative corresponding to the carboxylic. It has been discovered that,if the pH is adjusted in this manner so that there is no excessalkalinity, acid salts can in fact be hydrogenolyzed whereas they cannotbe when excess alkalinity is present. Likewise, if the pH is maintainedabove about 6, catalyst life is extended and apparatus corrosion isreduced as compared with conditions prevailing when the free acid itselfis hydrogenolyzed.

It has further been discovered that a particularly useful processresults when a potassium salt of the carboxylic acid is employed andwhen the desired buffering is accomplishedby maintaining a finiteconcentration of free carbon dioxide in the hydrogenolysis reactor (theresulting pH being that characteristics of the KHCO 2 CO equilibrium).At the conclusion of the hydrogenolysis reaction carried out with thispotassium salt: CO system, the liquid hydrogenolysis product is degassedat reduced pressure and at a temperature sufficient to decomposepotassium bicarbonate to potassium carbonate and carbon dioxide, wherebygaseous carbon dioxide is removed from the reaction product leavingbehind a liquid phase in which the potassium content exists mainly aspotassium carbonate. When the process is carried out in this manner witha hydrogenolysis product comprising predominantly a diol or diols havingat least about 4 carbon atoms or alkanols having at least about 3 carbonatoms, a particularly advantageous process results in that, bymaintaining in the hydrogenolysis product a potassium salt concentrationof at least about 2 gram-equivalents of potassium per kilogran of watercontained therein, it is possible to separate the organic hydrogenolysisproduct from an aqueous phase comprising water and the potassiumcarbonate by simply cooling the hydrogenolysis product mixture to atemperature at which two liquid phases form therefrom. The organicproducts can be recovered for whatever product workup process is desiredby simply decanting the upper, organic, layer while the lower, oraqueous, layer containing the potassium carbonate can be recycled to thehydrogenolysis step of the process. That is, the aqueous phase is mixedwith the carboxylic acid feedstock in sufficient quantity to prepare anaqueous solution thereof in which the carboxylic acid has beenneutralized in accordance with the reaction:

K CO RCOOH RCOOK KHCO It will be recognized, of course, that thecarboxylic acid in the foregoing equation can be a monocarboxylic or adicarboxylic acid as well as a hydroxycarboxylic acid or a lactone.

With reference to the phase separation mentioned above, the potassiumcontent of the mixture need not be as high as 2 gram-equivalents perkilogram of water when the hydrogenolysis product comprisespredominantly molecules having more than 2 carbon atoms per hydroxylgroup. Specifically, satisfactory phase separation obtains with onlyabout 1 gram-equivalent of potassium per liter of water when thehydrogenolysis product comprises a pentanediol or a higher homolog suchas 1,6-hexanediol. In accordance with the wellunderstood principles bywhich salt solutions have the effect of salting out" organic componentsof aqueous solutions, even lower concentrations of potassium salt (orother alkali metal salts) can be employed when the hydrogenolysisproducts are less hydrophilic than 1,6- hexanediol.

Detailed Description and Preferred Embodiments of the InventionFeedstocks In terms of commercial importance, the carboxylic acidfeedstocks to which the invention is particularly applicable comprisecarboxyalkanes, diearboxyalkanes, hydroxycarboxyalkanes, and lactones(which the cyclic esters of, and react during hydrogenolysis in the samemanner, as hydroxycarboxylic acids). Particularly useful feedstocks arethe carboxylic acids obtained by the liquid-phase oxidation ofcyclohexane, including succinic, glutaric, adipic, propionic, butyric,valeric, and caproic acids, epsilon caprolactone, and themonohydroxy-substituted derivatives of butyric, valeric, and caproicacid including specifically 6- hydoxyeaproic acid. Highercarboxyalkanes, dicarboxyalkanes, and hydroxycarboxyalkanes can also betreated. as well as the alkenoic acids. It will be recognized, ofcourse, that hydrogenolysis of the alkenoic acids may result information of the saturated hydroxymethyl-substituted derivatives.

Broadly speaking, any carboxylic acid which is a amenable to catalytichydrogenolysis can be hydrogenolyzed by the present process.

Buffering Systems The first step of the process is the neutralization ofthe free carboxyl groups of the carboxylic acid feedstock, the resultingsolution then being buffered to a pH between about 6 and 7. ln carryingout this step any of several approaches can be taken, which will beobvious to those skilled in the art. For example, as in a preferredembodiment of the invention, the carboxylic acid can be neutralized withan at least equimolar quantity of an alkali metal carbonate, especiallypotassium carbonate, with sufficient free carbon dioxide then beingadded to convert any residual carbonate to bicarbonate while maintaininga finite concentration of residual free carbon dioxide. Anotheralternative is to neutralize the carboxylic acid with a di-alkalai metalhydrogen phosphate. Other methods for preparing buffered solutions ofthe alkali metal salts of the carboxylic acid feedstocks will be readilyapparent, but the method just described entailing the use of an alkalimetal carbonate and free carbon dioxide is particularly useful. It willbe understood that during the hydrogenolysis step which follows thepreparation of the buffered salt solutions the conversion of carboxylatemoiety to hydroxymethyl moiety releases a quantity of alkalistoichiometrically equivalent to the converted carboxylate moiety. It isnecessary, therefore, that the weak acid component of the buffer systembe present in the hydrogenolysis reactor in at least sufficient quantityto neutralize this freed alkali while still maintaining a finitequantity of said weak acid component. For example, it is necessary thatwhen the weak acid component is carbon dioxide, there be maintained inthe hydrogenolysis reactor enough carbon dioxide to neutralize the freedalkali and still maintain an excess of free carbon dioxide (or carbonicacid).

Concentration of the components of the hydrogenolysis feedstocksolution, as distinguished from the stoichiometric relationships amongits components as discussed above, is not critical in the broaderaspects of the invention. However, concentration is a significantparameter in that embodiment in which recovery of the hydrogenolysisproducts is effected by deeantation of an organic liquid layer aspreviously discussed. Specifically, for that system in which potassiumcarboxylates have been hydrogenolyzed in the presence ofthe potassiumbicarbonate-carbon dioxide buffer system, it is recommended that, whenthe phase separation is carried out, there be present in the liquidproduct mixture at least about 1 gram-equivalent of potassium perkilogram of water contained in the mixture. This is sufficient to saltout" an organic phase comprising the hydrogenolysis product if theorganic phase comprises predominantly dihydroxy compounds having in themolecule at least about 2.5 carbon atoms per hydroxyl group ofmonohydroxy compounds having at least about 4 carbon atoms per hydroxylgroup (e.g., pentanediol and its higher homologs or butanol and itshigher homologs). If the hydrogenolysis product comprises predominantlya butanediol, e.g., l,4-butanediol, a somewhat high potassiumconcentration is recommended, i.e., at least about 2 gram-equivalentsper kilogram of contained water. Higher concentrations of dissolvedpotassium than those just named have no ill effect, of course, and willin fact enhance the degree of phase separation in marginal situations,i.e., when the hydrogenolysis product tends to be rather stronglyhydrophilic.

With further reference to the matter of concentration, water content ofthe hydrogenolysis feedstock solution is not critical although at leastenough water should be present to dissolve any components of thefeedstock which are normally solids, e.g., the carboxyl- HydrogenolysisThe details of how the hydrogenolysis step itself is carried out are notpertinent to the present invention except that this step of the processis carried out by the generally-understood processes for hydrogenolyzingliquid feedstocks comprising free carboxylic acids. Such a process isdescribed in British Pat. No. 921,477, which deals with thehydrogenolysis of aqueous or alcoholic solutions of a variety ofcarboxylic acids in the presence of sintered cobalt oxide which has beeprereduced with hydrogen before use in the hydrogenolysis process.Hydrogenolysis temperatures are in the range of 150 to 300C, preferably200 to 250C; hydrogenolysis pressure is about 5 to 500 atmospheres,especially 50 to 350 atmospheres. Pressure and temperature are, ofcourse, so correlated that a liquid phase is always maintained in thereaction chamber. These conditions are applicable in the hydrogenolysisstep of the present invention. Other forms of catalysts having acatalytically active metallic cobalt surface, e.g., fine cobaltprecipitated on inert supports such as stoneware, can also be employed;the invention is not restricted to use of the reduced sintered cobaltcatalysts, although these typify the presently available catalysts whichare generally employed for hydrogenolysis of free acids. Rhenium blackis also a suitable hydrogenolysis catalyst.

It will be recognized, of course, that in applying the present inventionin the hydrogenolysis reaction systems typical of the prior art, minormodifications will be made as necessary to allow for the fact that thereaction medium will contain alkali metal salts as well as organiccompounds. Specifically, sufficient water will be maintained in thereaction medium to assure that the carboxylate salts and any inorganicsalts which are present (e.g., potassium bicarbonate) will not beprecipitated from solution. Water concentrations as employed in thetypical prior art are sufficient for this purpose. Also, in that usefulembodiment of the invention in which carbon dioxide is a component ofthe buffer system, it will be understood that a finite quantity of freecarbon dioxide (or carbonic acid) is maintined in all portions of thehydrogenolysis reactor. As will be understood, the concentration f0carbon dioxide is not critical so long as a finite amount is present.When carbon dioxide is employed in this manner it can be added in itsentirety at the start of the reaction, i.e., incorporated into thehydrogen entering the reactor, or, if desired, distributed at severalpoints along the axis of the reactor (if the reactor be one of elongatedproportions). The quantity of carbon dioxide required is not of such amagnitude as to require any substantial elevation of reaction pressureto allow for the partial pressure of carbon dioxide incorporated intothe hydrogen gas phase.

It will be recognized also that the type of hydrogenolysis reactor to beemployed is not critical; any type suitable for the hydrogenolysisprocesses of the prior art is suitable, e.g., stirred autoclaves or,more preferably, vertical vessels or tubes through which the liquidfeedstock is passed and within which it is contacted with hydrogen andthe catalyst, typically positioned in the reactor as a packed bed ofpellets or catalyst-coated supports such as Berl saddles.

Product Recovery In its broader aspects the invention is not restrictedto any particular method for recovering the organic products of thehydrogenolysis reaction. The liquid product withdrawn from thehydrogenolysis reactor comprises one or more hydroxy compounds,,typically alkanols, alkanediols, or both, along with some water and aquantity of inorganic salts. When it comprises but a single phase, andwhen the buffering system being employed is not one in which potassiumbicarbonate decomposition is, for example, employed to salt out theorganic components, conventional methods can be employed to recover theorganic products. For example, the organic products can be separatedfrom the water and the inorganic salts by solvent extraction with, forexample, an ester such as a lower alkyl carboxylate, followed bydistillation if desired. The inorganic buffering agent or agents canthen be recycled, if desired, to the neutralization and hydrogenolysissteps of the process.

In the preferred embodiment of the invention, however, the potassiumbicarbonate-carbon dioxide buffering system is employed in thehydrogenolysis, with the result that the hydrogenolysis productcomprises alkanols and/or alkanediols, water, and potassium bicarbonatealong with some dissolved carbon dioxide. It will be understood, ofcourse, that some hydrogen may also be present until the product hasbeen degassed; any such excess hydrogen will, of course. typically beseparated from the reaction product before workup ot' the liquid productitself.

The liquid hydrogenolysis product may or may not exist in a singleliquid phase as it is withdrawn from the reactor. If there are twoliquid phases, they can be handled together during the degassing andproductseparation steps which are to follow.

The first step is to degas the liquid reacton product, at a temperaturehigh enough to thermally decompose aqueous potassium carbonate topotassium carbonate, while maintaining a sufficiently high pressure toretain the bulk of the reaction product in the liquid phase. Therequired temperature is in the range of about C to 110C, with about to107C being particularly suitable. At these temperatures, substantiallyatmospheric pressure can be employed. Higher temperatures can beemployed if desired, with correspondingly higher pressures beingemployed to maintain an aqueous liquid phase in the material beingdegassed. The evolved carbon dioxide is vented from the degassingreaction vessel and is either discarded or, if vessel land is eitherdiscarded or, if desired, recycled to the hydrogenolysis reactor. Itwill be recognized that complete decomposition of all the potassiumbicarbonate contained in the reaction product to potassium carbonate isnot essential; undecomposed bicarbonate can be recycled to thehydrogenolysis reaction step if desired, so long as sufficient carbonateis provided to neutralize all of the fresh carboxylic acid feedstockwhich is to be hydrogenolyzed in the hydrogenolysis step of the process.In batch degassing, the bicarbonate-decomposition step is carried out byholding the liquid at the desired degassing temperature until carbondioxide evolution has substantially ceased. ln continuous operationsthis step can be controlled by coordinating degassing temperature andretention time at such levels that carbon dioxide is evolved at a ratesuch that substantially the entirety of the potassium bicarbonate fedinto the degasser is converted to potassium carbonate.

After degassing, the liquid reaction product is cooled as necessary toeffect its separation into two liquid pha ses. With higher molecularweight hydrogenolysis products such phase separation may take place, orat least take place to some extent, at the degassing temperature, i.e.,at about 100C. With lower molecular weight products, however, cooling isnecessary to effect phase separation and, even with higher molecularweight products, cooling is recommended to enhance the efficiency of theseparation. More particularly, it is recommended that the degassedliquid be cooled to roughly 40C for optimal phase separation efficiency.

After the phase separation has occured, the lower or aqueous, layer isadvantageously employed again for neutralizing the carboxylic acidfeedstock. It will be recognized that in some circumstances it may bedesirable to remove water-soluble organic impurities from this aqueousphase to prevent their buildup in the reaction system. The upper, ororganic phase is forwarded to product purification steps which areoutside the scope of the invention and which will vary according to thenature of the hydrogenolysis product but which typically comprisedistillation to separate the mixture into its various components asdesired.

In connection with the foregoing discussions of the hydrogenolysis andproduct recovering steps it should be noted that it is not essentialthat the hydrogenolysis step of the process be carried entirely tocompletion; that is there is no disadvantage if the reactor product fromthe hydrogenolysis step still contains a portion of unreactedcarboxylate salts of the carboxylic acid feedstock. In the processemploying potassium carbonate and subsequent phase separation of theproduct, such carboxylate salts partition strongly into the aqueousphase, with the result that they are easily recycled with the aqueousphase to the neutralization and hydrogenolysis steps of the process.Thus the unconverted car boxylate moiety is both separated from therecovered organic products (the organic layer formed in the phaseseparation) and also recycled for further hydrogenolysis. The result isthe maintainenanee of a high hydrogenolysis reactor throughput (reactorvolume for, say, 90 percent conversion being ordinarily much less thanthe volume required for, say, near-100 percent conversion) and also areduction in corrosion in the product purification apparatus which wouldotherwise take place if free carboxylic acid were present in the crudeorganic products being distilled or otherwise processed.

The following examples are given to further illustrate the practice ofthe invention; it will be recognized that many variations can be madetherefrom within the scope of the invention.

Example I As hydrogenolysis feedstock there was employed a crude mixtureof carboxylic acids obtained by the liquid phase oxidation ofcyclohexane and containing, by weight, approximately 20% of adipic acid,2% succinic acid, 4% glutaric acid, 6-hydroxycaproic acid andepsilon-caprolactone, and the remainder a mixture of otheralkanecarboxylic acids, dicarboxylic acids, and

hydroxycarboxylic acids of less than 6 carbon atoms per molecule derivedfrom the oxidation of cyclohexane.

The feedstock just described was dissolved in a methanol-water mixturecontaining 25 weigth percent methanol and the remainder water, to make a10 percent solution. The methanol was employed for the purpose ofsimplifying the measurement and analysis of the anticipatedhydrogenolysis product by prevent the formation therein of two liquidphases.

The solution just described was neutralized with disodium hydrogenphosphate, to a pH ofabout 6.2 as measured at room temperature. Theneutralized solution was then placed in a rocking autoclave containing.per ml of the solution, approximately 30 grams of 3/l6-inch diameterpellets of a sintered metallic cobalt catalyst formed by reducingsintered cobalt oxide pellets with hydrogen according to the methodscustomarily employed in the prior art (e.g., as in British Pat. No.921,477) for preparing and conditioning such catalysts. The contents ofthe autoclave were then treated with hydrogen for about 4 hours at 230Cand at about 300 atmospheres of hydrogen pressure.

Upon cooling the autoclave, releasing the hydrogen, and analyzing theliquid product, it was determined that, within the limits of analyticalaccuracy, all of the carboxyl moiety in the feedstock had been convertedto hydroxymethyl moiety. Substantially all of the adipic acid,hydroxycaproic acid, and caprolactone had been converted tol,6-hexanediol.

Example ll The same feedstock solution employed in Example I wasneutralized with potassium carbonate instead of disodium hydrogenphosphate. Approximately l mole of potassium carbonate was employed perequivalent of carboxyl moiety in the feedstock. The neutralized solutionhad a pH of approximately 8.0. Potassium bicarbonate was then added, inan amount of 1 mole per mole of potassium carbonate.

The neutralized solution was placed in the same autoclave as employed inExample I along with the same catalyst, the ratio of catalyst toreactant solution being the same also as in Example I. Additionally,approximately 2 grams of solid carbon dioxide was placed in theautoclave per 100 ml of reactant solution. Carbon dioxide was added inthis manner instead of as carbon dioxide gas for the sake ofconvenience. After addition of the carbon dioxide the pH of theresulting mixture was between 6.0 and 7.0.

The autoclave containing reactant liquid, catalyst, and carbon dioxidewas then pressured with hydrogen and the hydrogenolysis reaction wascarried out as in Example I. Analysis of the liquid products indicatedthat hydrogenolysis of the carboxy moiety of the feedstock was completeas in Example I.

Example III A carboxylic acid feedstock identical with that described inExamples l and II is mixed with water and potassium carbonate to form asolution containing approximately l0.0 weight percent organic material,70.0 weight percent water, 10.0 weight percent potassium bicarbonate,and 10.0 weight percent potassium carbonate. In this mixture thecarboxylic acid content of the organic feedstock is, of course, presentas the potassium salts.

Carbon dioxide is then bubbled through the solution prepared as justdescribed in an amount at least sufficient to convert all the potassiumcarbonate present to potassium bicarbonate.

The neutralized solution is then placed in an autoclave with ahydrogenolysis catalyst as described in Examples l and II, along withcarbon dioxide in an amount equal to at least one mole thereof perequivalent of potassium carboxylate contained in the feedstock solution.The autoclave is then pressured with hydrogen and the feedstockhydrogenolyzed as in Examples 1 and 11.

After hydrogenolysis the atuoclave cooled to approximately 40C, thehydrogen is released, and the liquid contents are drawn off into aseparate vessel in which they reheated to approximately 100C. Heating iscontinued until gas evolution from the liquid has the lower phasecomprises predominantly water containing dissolved potassium carbonate.The upper phase is drawn off for workup of the organic products asdesired, while the lower phase is drawn off for reuse in neutralizingadditional quantities of the carboxylic acid feedstock as previouslydescribed.

Of the carboxylic acid moiety contained in the crude feedstock prior toneutralization, approximately 95 percent is recovered in the form of thecorresponding hydroxymethyl derivatives in the organic phase obtainedafter the degassing step just described. Any unconverted potassiumcarboxylate is recycled to the hydrogenolysis step with the aqueouslayer obtained after the phase-separation step and is so ultimatelyrecovered as the desired hydroxymethyl-substituted product.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a process for converting a feedstock comprising predominantly atleast one member of the group consisting of carboxyalkanes,dicarboxyalkanes, hydroxycarboxyalkanes, and lactones ofhydroxycarboxyalkanes having at least four carbon atoms in the moleculeto a corresponding hydroxymethyl-substituted derivative by thehydrogenolysis of the carboxy moiety of said feedstock in the presentofa rhenium black catalyst or a catalyst having a catalytically activemetallic cobalt surface, the improvement which comprises:

preparing an alkali metal salt of said feedstock in aqueous solution;.buffering said solution of said salt to a pH between about 6.0 and about7.0;

hydrogenolyzing said salt in said buffered solution in the presence ofsaid catalyst at a temperature of C to 300C and at a pressure of about 5to 500 atmospheres to form a liquid reaction product comprising saidhydroxymethyl-substituted compound; and

recovering said hydroxymethyl-substituted compound from said reactionproduct.

2. The process of claim 1 wherein the buffering system employed is analkali metal bicarbonate system or an alkali metal acid phosphatesystem.

3. The process of claim 2 wherein the catalyst employed in saidhydrogenolysis step comprises metallic cobalt.

4. The process of claim 3 wherein said salt solution is buffered withcarbon dioxide and the bicarbonate of said alkali metal.

5. The process of claim 4 wherein said alkali metal is 132$ UNITEDS'IAIIZS PA'IEII'I OFFICE CERTIFICAISIQ OF comsorrow Patent No.3,855,319 Dated December 17, 1974 Inventofls) Charles C. Hobbs, John ABedford It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

In column 1, line 30, or'"diods" read diols In column 1, line 33, for"simply" read simple In column 1, line 59, for "orocess" read processesIn column 1, line 61, for "relation" read related insert acid In column2, line 50, for "characteristics" read characteristic In column 4, line10, for "alkalai" read alkali In column 6, line 43, at first occurrenceof the word "carbonate" read --bicarbonate--.

In column 6, lines 55-56, delete "if vessel land' is either discardedor,

In column 8, line 5, for "weigth" read weight I In column 8, line 9, for"prevent" read preventing In column 9, line 13, for "atuoclave" readautoclave is Signed and sealed this 1st day of April 1975.

QLiiin Attest:

C. T-IARSHALL DAMN n r* v1 IIUIL c, HAQOI. Commissioner of Patentsz.ttesting Officer and Trademarks

1. IN A PROCESS FOR CONVERTING A FEEDSTOCK COMPRISING PREDOMINANTLY ATLEAST ONE MEMBER OF THE GROUP CONSISTING OF CARBOXYALKANES,DICARBOXYALKANES, HYDROXYCARBOXYALKANES, AND LACTONES OFHYDROCARBOXYALKANES HAVING AT LEAST FOUR CARBON ATOMS IN THE MOLECULE TOA CORRESPONDING HYDROXYMETHYL-SUBSTITUTED DERIVATIVE BY THEHYDROGENOLYSIS OF THE CARBOXY MOIETY OF SAID FEEDSTOCK IN THE PRESENT OFA RHENIUM BLACK CATALYST OR A CATALYST HAVING A CATALYTICALLY ACTIVEMETALLIC COBALT SURFACE, THE IMPROVEMENT WHICH COMPRISES: PREPARING ANALKALI METAL SALT OF SAID FEEDSTOCK IN AQUEOUS SOLUTION; BUFFERING SAIDSOLUTION OF SAID SALT TO A PH BETWEEN ABOUT 6.0 AND ABOUT 7.0;HYDROGENOLYZING SAID SALT IN SAID BUFFERED SOLUTION IN THE PRESENCE OFSAID CATALYST AT A TEMPERATURE OF 150*C TO 300*C AND AT A PRESSURE OFABOUT 5 TO 500 ATMOSPHERES TO FORM A LIQUID REACTION PRODUCT COMPRISINGSAID HYDROXYMETHYL-SUBSTITUTED COMPOUND; AND RECOVERING SAIDHYDROXYMETHYL-SUBSTITUTED COMPOUND FROM SAID REACTION PRODUCT.
 2. Theprocess of claim 1 wherein the buffering system employed is an alkalimetal bicarbonate system or an alkali metal acid phosphate system. 3.The process of claim 2 wherein the catalyst employed in saidhydrogenolysis step comprises metallic cobalt.
 4. The process of claim 3wherein said salt solution is buffered with carbon dioxide and thebicarbonate of said alkali metal.
 5. The process of claim 4 wherein saidalkali metal is potassium.